Apparatus for slip casting ceramic electrical ware



Dec. 28, 1965 APPARATUS FOR SLIP CASTING CERAMIC ELECTRICAL WARE Filed Nov. 1, 1962 INVENTOR. JZ/m .Uean

United States Patent 3,225,414 APPARATUS FOR SLIP CASTING CERAMIC ELECTRICAL WARE John Dean, Kenova, W. Va., assignor to McGraw-Edison Company, Milwaukee, Wis., a corporation of Delaware Filed Nov. 1, 1962, Ser. No. 234,823 3 Claims. (Cl. 25-129) This invention relates to forming ceramic parts and more particularly to an improved apparatus for slip casting.

The two common methods of slip casting objects are to admit casting slip into a porous mold or through casting wells disposed in either the top or bottom of the mold. Use of a casting well in the top of the mold may result in the entrapment of air during the pouring of the slip resulting in ware of less density with lower mechanical and electrical strength. In molds which contain a core there is an additional disadvantage in that streamers are often caused along the core which require a further finishing operation for their elimination. It is also possible that streamers which build to an excessive thickness will result in an inherent stress causing impairment of the mechanical and electrical properties of the fired ware.

Injecting casting slip through a well near the bottom of the casting mold overcomes the difficulties mentioned above, since air is forced out of the mold cavity ahead of the incoming casting slip while the level of slip is simultaneously raised in such a manner that streamers are not formed. The conventional manner of injecting casting slip through such a bottom casting well is to connect the casting well to a supply of slip which is maintained under pressure during both the filling operation and thereafter until the ware has been cast. After the mold is filled it is necessary to make up the shrinkage in volume caused by moisture being taken up from the slip by the porous mold.

Casting wells, through which casting slip is fed, cause defects. This is true whether the mold is fed through a casting well in the top of the mold or through a well in the bottom of the mold. The defects appear as areas of excessive shrinkage, cracks, and low mechanical and electrical strength. Sometimes open voids will occur beneath the surface in the area of the casting well which cannot easily be detected short of destructive inspection which destroys the Ware.

The apparatus of the present invention utilizes a casting well near the bottom of the mold cavity which eliminates the difliculties encountered when filling from the top. Further, the defects described as incident to the use of casting wells are avoided by interrupting flow through the lower casting well and thereafter allowing the mold to be filled during the casting operation through a casting well that communicates with a part of the cavity that forms a portion of the finally formed object which will be trimmed away. By so doing the defects caused by the casting well are removed with the trimmed waste portion to yield an article of ware free of such defects.

It is an object of this invention to provide an improved apparatus for slip casting ceramic Ware.

It is a further object of this invention to provide an apparatus for slip casting that avoids both streamers caused by filling the mold from the top and structural defects arising from the use of a casting Well.

These and other objects and advantages of this invention will become apparent from the following description when taken in connection with the accompanying drawings, wherein:

FIG. 1 is an elevation view in partial section of the mold of this invention;

"ice

FIG. 2 is a section taken along line IIII of FIG. 1;

FIG. 3 is a partial elevation, partially in section with the cap portion of the mold removed showing part of the newly cast shape before the latter has been trimmed; and

FIG. 4 is an elevation partially in section of the completed ware formed by the mold of FIG. 1.

Referring to FIG. 1 an upright porous mold 10 is shown having a pair of mating outer mold sections 11, which are retained in position with respect to. one another by the bands 13. The mold sections 11 are supported on a base ring 15 and extending upwardly through the center of the base ring and positioned thereby is a central core 16. Above the mold sections 11 is a cap or auxiliary cavity forming portion 13 and a reservoir 20 which is in fluid communication with the auxiliary cavity portion 22 through the casting well 23.

Through a lower portion of one of the mold sections 11 is a second casting well 25, which has a supply conduit 27 connected thereto. As seen in FIGS. 1 and 2, a rectangular passage 29 intersects the casting well 25. A cooperating rectangular gate 30 having a passage 31, therethrough is slidably disposed in the passageway 29 for movement between a position where passage 31 is aligned with the casting well 25 and a position whereby the gate 30 interrupts fluid communication between the conduit 27 and the ware forming cavity portion 33. The gate 30 is preferably made of the same material as the mold section 11 to afford as nearly as possible a uniformity throughout the material of the mold section.

The configuration of the formed object is determined by the cavity bounded by the mold sections 11, the cap 18, base ring 15, and core 16 which would yield an object defined by the composite of the cavity portions 22 and 33. Each of the above indicated mold portions which surround the object forming cavity are made of a porous material such as plaster of Paris.

In the present embodiment the ultimately finished ware is identical to the cavity portion 33 surrounded by the mold sections 11 and an auxiliary object portion is formed by the cavity portion 22 within the cap 18. The composite object cast in the mold is without a severe change in cross section at the juncture of ware forming cavity and the auxiliary cavity. Specifically it is to be noted that the cross section of the ware forming cavity 33 immediately below the cap 18 and the cross section of the cavity 22 immediately above the mold sections 11 are substantially the same. Further as shown in the preferred embodiment, the casting Well 23 communicates with the cavity 22 at the location most remote from the cavity 33.

Utilizing the apparatus described above an article of ware is formed by supplying casting slip to the mold as assembled in FIG. 1 so that the level of slip, rising from the bottom of the mold cavity portion 33, fills both cavity portions 22 and 33 and causes sufiicient casting slip to enter the reservoir 20 to both provide make up slip and apply a hydrostatic pressure to the object forming cavity portions during the balance of the casting operation. The gate 30 is then moved to interrupt fluid communication through casting well 25 and make up slip is supplied from the reservoir 20 through casting well 23 during the balance of the casting operation.

When the cast object has become sufliciently solidified for further processing, it is removed from the mold and the auxiliary portion trimmed from the ware. In the embodiment shown, because the ware forming portion of the mold is coextensive with the mold sections 11, the trimming operation can be simplified by removing the cap 18 and core section 16, and thereafter trimming the object, using the top surfaces 35 (FIG. 3) of the mold sections 11 as a guide.

The resulting ware as shown in FIG. 4 is free from streamers, particularly adjoining the core of the mold, by reason of filling from the bottom of the mold and avoids the defects occasioned in the vicinity of the casting well by feeding slip to the cavity at a location remote from the ware forming portion to cause any such defects to occur in a portion trimmed from the object and discarded.

While a single embodiment of the invention has been shown and described, it is not intended that the invention should be limited thereto, but should include such other embodiments and variations as come within the scope of the appended claims.

I claim:

1. A mold for slip casting ceramic objects comprising: a lower object forming porous mold portion defining a vertically extending cavity, having a casting Well communicating with said cavity through an upper Wall of said object forming portion; a reservoir disposed above said object forming mold portion in fluid communication with said cavity through said casting well; a lower passage extending through said object forming mold portion in fluid communication with said cavity adjacent to the lowermost portion thereof, and selectively operable closure means movable transversely of said lower passageway to interrupt fluid communication through said lower passage.

2. A porous mold for slip casting ceramic ware comprising a vertically extending cavity, said cavity including a lower ware forming portion and an upper auxiliary portion communicating with said ware forming portion substantially throughout the area of the upper terminal end of said ware forming cavity portion; an upper casting well communicating with said auxiliary cavity portion at a location remote from said ware forming cavity portion; a reservoir extending upwardly from said mold and communicating with said cavity through said upper casting Well; a fluid passageway communicating with said cavity adjacent to the lowermost portion thereof; and selectively operable closure means for interrupting fluid flow through said passageway comprising a transverse passageway in said ware forming mold portion intersecting said fluid passageway and a gate member formed of a material having a porosity similar to the porosity of the associated Ware forming mold portion, said gate being slidable into and out of a position wherein fluid communication through said fluid passageway is interrupted.

3. A mold for slipcasting ceramic ware comprising a lower ware forming porous mold section defining a vertically extending cavity; an upper auxiliary porous forming section which is in fluid communication with said ware forming section substantially throughout the entire area of the upper end of said ware forming cavity section; a casting well communicating wtih said cavity through said auxiliary portion at a location remote from said ware forming portion; a passageway through said mold in fluid communication with said ware forming cavity section adjacent to the lowermost portion thereof; and selectively operable closure means for interrupting fluid flow through said passageway, said closure means including a gate formed of the same material as said ware forming section of said cavity and slidable transversely of said passageway between a position permitting continuous fluid communication through said passageway and a position interrupting fluid communication through said passageway.

References Cited by the Examiner UNITED STATES PATENTS 1,304,571 5/1919 Kirk et al. 264-86 1,564,274 12/ 1925 Rand 264-86 1,882,191 10/1932 Purinton 246-86 2,261,583 11/1941 Hemphill 264-219 2,288,661 7/1942 Wadman 264-86 ROBERT F. WHITE, Primary Examiner.

ALEXANDER H. BRODMERKLE, Examiner. 

1. A MOLD FOR SLIP CASTING CERAMIC OBJECTS COMPRISING: A LOWER OBJECT FORMING POROUS MOLD PORTION DEFINING A VERTICALLY EXTENDING CAVITY, HAVING A CASTING WELL COMMUNICATING WITH SAID CAVITY THROUGH AN UPPER WALL OF SAID OBJECT FORMING PORTION; A RESERVOIR DISPOSED ABOVE SAID OBJECT FORMING MOLD PORTION IN FLUID COMMUNICATION WITH SAID CAVITY THROUGH SAID CASTING WELL; A LOWER PASSAGE EXTENDING THROUGH SAID OBJECT FORMING MOLD PORTION IN FLUID COMMUNICATION WITH SAID CAVITY ADJACNET TO THE LOWERMOST PORTION THEREOF, AND SELECTIVELY OPERABLE CLOSURE MEANS MOVABLE TRANSVERSELY OF SAID LOWER PASSAGEWAY TO INTERRUPT FLUID COMMUNICATION THROUGH SAID LOWER PASSAGE. 